Fluorescence correlation spectroscopy (FCS) implemented in a microscope construction (FCM) has proven successful for investigating biomolecular interactions particularly where the investigations are carried out in very small ranges of concentration of less than 1 μmol and in measurement volumes of less than 10−14 1. The measurement location plays only a minor role, provided the specimens to be examined are homogeneous. However, in connection with structured specimens such as biological cells, knowledge and selection of the measurement location is critically important. Formerly, this knowledge of the measurement location was gained by conventional transmitted-light and incident-light microscopy. For this purpose, switching was carried out between the FCS detection unit and a conventional fluorescence microscope arrangement. The use of conventional microscopy has several disadvantages. On the one hand, the specimens are exposed to high radiation loading; on the other hand, the optimal measurement location can not be localized in three-dimensional coordinate systems with the required accuracy of less than 1 μm.
The arrangements and methods described and claimed below, with reference to the drawings, advantageously make it possible to expand the FCS method to an imaging method (S-FCM). In this way, information can be gained concerning the spatial distribution of the molecular interactions under investigation.